Add publisher artwork to GitHub APK source entries

Include curated app images and summaries, owner avatars and social banners for topic discovery, and fixture coverage for artwork preservation.

Co-Authored-By: GPT-6 Astra <noreply@openai.com>

tests/fixtures/more_sources/README.md

@@ -13,3 +13,11 @@ values are unchanged. No token, cookies or signed download URL is included.
 The synthetic ZIP in tests is only a transport/integrity fixture, not an
 installable APK. Actual APK parsing was verified separately on the downloaded
 Khronos Vulkan sample; see docs/apk-sources.md.
+
+Artwork follow-up: `topic.json` now retains `owner.avatar_url` from authenticated
+repository API reads. `artwork-check.json` records HTTPS response status,
+Content-Type and image magic checks for all curated URLs and three topic
+results. All curated URLs returned real images; LWJGL's social preview returned
+HTTP 429. This fixture is evidence of a point-in-time check, not an uptime test.
+Open Brush screenshots came from the Steam appdetails response for app 1634870,
+linked by its README. SuperTux's README links the recorded upstream screenshot.